The major objective is to elucidate the role of early nutritional experiences on the developmental aspects of carbohydrate and lipid metabolism and the subsequent effect on adult adiposity and muscularity. This can be studied best in genetically obese rodents where a measurable sequel is known both at the gross and at the biochemical levels of organization. Three varieties of genetic obesity will be used; the obese hyperglycemic mouse (ob/ob), the yellow obese mouse (Ay/a), and the fatty rat (fa/fa). These animals will be studied from the pre-obese phase of development through fully blatant obesity. Very young genetically obese animals will be identified prior to the genetic expression of obesity. During the pre-obese and subsequent phases of development, the major sites of lipogenesis and enzymatic profiles of liver and adipose tissue will be evaluated to ascertain whether the major site of lipogenesis shifts from liver to adipose tissue as development proceeds. The roles of high carbohydrate and high fat diets, initiated during the pre-obese phase of development, will be evaluated for their effectiveness to influence the development of obesity and its metabolic consequences. The relationship between adiposity and muscularity will be examined as development proceeds. Additionally, investigations are proposed to determine whether an intrinsic defect exists in the musculature of these animals, which effectively limits the availability of energy utilization for muscle growth, thereby directing this energy to lipid storage in adipose tissue. The results of the proposed investigations should increase our understanding of the interaction of early dietary experiences and neonatal development, particularly with regard to the development of obesity.